This invention relates to inhibiting the freezing of water on coal and other particulate products, to maintain a substantially free-flowing state under otherwise subfreezing conditions. Under the influence of the invention, ice crystals which may be formed are weaker than would otherwise would be the case, also tending to maintain a substantially free-flowing state in coal piles and in other accumulations of particulate materials to be moved.
Coal is stored, shipped and transferred in many locations having cold climates and in areas likely to experience temperatures below the freeze point of water. Most material handling equipment is designed to handle free-flowing materials, not materials which are frozen together in large chunks. Entire piles of coal have been known to accumulate significant amounts of water which may continue to accumulate over a period of days and become almost monolithic, frustrating efforts to break them apart and ship or transfer without extraordinary efforts.
The problem is stated succinctly by Parks et al in U.S. Pat. No. 4,117,214, column 1, lines 22-36: xe2x80x9cFor example, coal with as little as 4% moisture will, when frozen, cohere so strongly as to require special handling to break up the frozen mass. It thus becomes difficult to unload or dump railway cars, trucks and other conveyances used to transport coal, mineral ores and other finely divided solids. It also makes difficult the movement of coal out of outdoor coal storage piles in a condition for fuel or other use. Unloading frozen coal from railroad cars is time consuming, can result in blocked dump chutes and can often leave as much as 30 to 60 tons of coal in the car. Various techniques such as vibration, steam lances, fires under the cars, infrared heating in warming sheds and even dynamiting have been tried to unload frozen cars.xe2x80x9d Parks et al go on to suggest applying to the coal a solution of a non-volatile organic compound and a water-soluble polyhydroxy compound or monoalkylether thereof, in order to weaken the ice that is nevertheless formed.
We have found that applying a solution of potassium formate on a pile or other mass of coal, minerals or other solid particulate material will inhibit the formation of coherent ice in the interstices of the particulate material. The effects of a solution of potassium formate are three: the freeze point of water is reduced, thus inhibiting the formation of ice; where ice is nevertheless formed in the presence of potassium formate, it is weaker than ice formed in the absence of potassium formate, and, if ice has already been formed prior to the application of potassium formate, the application of potassium formate will melt the ice.
Preferably the potassium formate solution is applied prior to the onset of snow or freezing rain. It may be applied in any effective manner, such as by pouring, but spraying is preferred. A spray may be conducted so that the coal or other particulates are wet with the solution at the time the snow or freezing rain arrives, or so that the water from the solution has evaporated by the time the precipitation arrives, leaving a residue of potassium formate on the particulates. In the former case, (prior to the arrival of precipitation), the still liquid solution of potassium formate on the surface of the particulates may be diluted with moisture from the snow in immediate contact with it before the pile is covered with snow, but the effect is that if ice forms, an underlayer of potassium formate solution is actually in contact with the coal or other particulate surface, and the freeze point of the solution is thereby reduced. Even when or if there are cycles of thawing and freezing, the concentration of potassium formate remains highest at the surface of the coal, mineral or other particulates, greatly decreasing the tendency of the weakened ice which does form to coalesce a large portion of the pile or other mass.
In the second case, where the potassium formate solution is sprayed on the previously formed ice or frozen mass of ice and snow, the solution will tend to dissolve the frozen mass, because of its lower freezing point.
In a third variation of the invention, finely divided solid potassium formate is sprinkled on the pile or mass of particulates prior to precipitation likely to form a frozen mass in the interstices of the particulates.
The term xe2x80x9cparticulatesxe2x80x9d is used herein to refer to both small and large substantially water-insoluble particles, ranging from finely ground material to large lumps such as large lumps of coal, and includes materials and ores having a wide range of hardness and moisture contents.